Feb 8th-9th Do We Finally Get A Coastal?

[phil882]

One thing that often gets unnoticed but has a pretty substancial impact this time of the year with regards to mid-latitude synoptic systems is the strength of oceanic subtropical ridging. This gets mentioned a lot during the summer TC season because the strength of subtropical ridging often is the difference between a recurving TC vs. one that might have its sights on a US landfall. 

 

However, their subtle impact in the winter season is probably one that gets overlooked. And we had a brilliant example of that occurring in the disparity in the model guidance yesterday. Lets look at two particular geopotential contours at 500 hPa from the 00z ECMWF and GFS yesterday forecast at 96 hours.

 

 

Here we are investigating the 576 dm to get a sense of the subtropical flow, and the 540 dm geopotential height to get a sense of the polar flow. Note that there is actually quite a bit of agreement with the GFS and ECMWF with regards to the strong upper level trough expected to dig into the Pacific NW next week. Where the greatest disagreement lies though is in subtle shifts in the flow downstream, especially eastward of this next polar impulse. Note the subtle ridge off the East US coastline on the ECMWF while the GFS is flat if not showing a trough off the east coast. We all know even in winter, the subtropical ridge likes to rear its ugly head, but in this case, the subtle ridging on the ECMWF is actually helping to promote a more meridional flow regime that could aid cyclogenesis greatly over and off the eastern US coastline. 

 

We talk about this all the time, but sometimes you can go from a merely ordinary shortwave into to something quite dynamic if we get some degree of phasing between the subtropical and polar jets. In the example above, its suggested that the ridging off the east coast allows this potential to be realized with the ECMWF. The GFS can't merge the energy because the flow is too zonal which limits the meridional component of the subtropical shortwave. It really is the subtropical shortwave that is the magic ingredient in this case, because its also providing all the straiform convection that is necessary for mid-level diabatic heating. Diabatic heating from both convective and stratiform precipitation can lead to positive geopotential height perturbations which allow for further ridge amplification. Its a non-linear process that once kicked off, often leads to robust cyclogenesis. 

 

So in short, the Euro is more robust with subtropical ridging, which allows the southern stream shortwave to be strong enough to produce a large precipitation shield, both convective and stratiform. Thanks to this diabatic forcing, the ridge is further amplified, and now the entire system can grow from baroclinic processes (extracting energy from the temperature gradients generated from meridional flow).

 

Since the typical bias is to be too weak with subtropical ridging over the Atlantic, I wouldn't be suprisied to see the GFS continue to trend towards the ECMWF on this particular solution. 

[Typhoon Tip]

Hate seeing that 84 hrs out. 

 

 

I think we are going to be okay on this one  

[Zeus]

Hate seeing that 84 hrs out. 

 

Exactly. Even 48, these days, would seem to have too much wiggle room.

 

Undoubtedly things fluctuate from here to Thursday night, but in what direction?

 

Here's hoping we keep the "good" (banana high, phase) relatively intact.

[CoastalWx]

i wonder if it actually has the room though. i'm not sure it does. unless the timing is fairly f-ed up. 

 

 

I would think there would be a pretty awesome ageostrophic northerly wind near the surface in that set up.

 

Definitely would be ageo flow, but lots of time left too. Srn stream systems though are sneaky. That's a crazy H5 evolution...so delicate too.

[It's Always Sunny]

Whoever went down with the key and unlocked the gulf, thank you

USAAFWEATHER

[Baroclinic Zone]

i wonder if it actually has the room though. i'm not sure it does. unless the timing is fairly f-ed up. 

 

I actually agree with you here.  With the confluence to the N, there is only so far N this thing will come.  What a beautiful solution that is.  Love the N stream capture which slows the system ever so slightly.  Also, I must add.  RESPECT the southern stream juice.

[Zeus]

Bus will be long gone...lol

 

Yes, but possibly headed for Dead Man's Curve on a one-way trip.

 

I'm not new to the game. Things are interesting, and that's about it.

[dryslot]

Definitely would be ageo flow, but lots of time left too. Srn stream systems though are sneaky. That's a crazy H5 evolution...so delicate too.

 

 

Its going to have to be timed just right for the big end result

[earthlight]

One of the more odd looking, and fast, phases between two pieces of energy at 500mb. But it turns into an absolute nuke once that southern stream gets involved and the mid level centers close off.

[Clinch Leatherwood]

Better than 96

 

Yeah for once things are improving inside of 96 assuming the Euro stays on board.

Yes, but possibly headed for Dead Man's Curve on a one-way trip.

I'm not new to the game. Things are interesting, and that's about it.

Looks good for now and the trend has been good. But like you said....

[Patrick-02540]

That's 1-2 feet regionwide.

Here we go.

[dryslot]

Yes, but possibly headed for Dead Man's Curve on a one-way trip.

 

I'm not new to the game. Things are interesting, and that's about it.

 

Nice to see, But not totally bought in, Lot of time still out there

[CoastalWx]

Yeah Phil, the euro has been more robust with that ridge...I noticed that yesterday. Certainly helps out with getting the s/w further north and then dynamics do the rest as you described. That's why srn stream systems have my attention. 

[ctsnowstorm628]

Looks pretty borderline to me...and at 3 days out...its hard to be too optimistic.

Really hard to get too excited this far out, especially near the coast. In this cold season, NW has been the rule inside 72 hours.

The HP to the north should help to limit the westward extent of this though. Even though a track over the outer cape wouldn't shock me.

Also the southern stream would need to go bonkers for this to get mega amped which probably won't happen.

[OSUmetstud]

Definitely would be ageo flow, but lots of time left too. Srn stream systems though are sneaky. That's a crazy H5 evolution...so delicate too.

 

any KUs you know of with a similar evolution?

[OSUmetstud]

where is Ray? 

[dryslot]

I actually agree with you here.  With the confluence to the N, there is only so far N this thing will come.  What a beautiful solution that is.  Love the N stream capture which slows the system ever so slightly.  Also, I must add.  RESPECT the southern stream juice.

 

 

Of course

[CoastalWx]

I'm not suggesting rain, but It's possible it can track closer....I suppose the opposite can be true too. 

[Baroclinic Zone]

Who cares if you taint in this one?  I'll take this sort of system any day over the crap we've been tracking all winter.

[CoastalWx]

any KUs you know of with a similar evolution?

 

Not off the top of my head..maybe Will might know. It's a funky setup.

[ORH_wxman]

Really hard to get too excited this far out, especially near the coast. In this cold season, NW has been the rule inside 72 hours.

The HP to the north should help to limit the westward extent of this though. Even though a track over the outer cape wouldn't shock me.

 

I would actually say that this is the opposite of what has actually happened in most events.

[CoastalWx]

Phil gets a fooking hurricane.

[N. OF PIKE]

Yes, but possibly headed for Dead Man's Curve on a one-way trip.

 

I'm not new to the game. Things are interesting, and that's about it.

i think that's where alot of us will fall later today, cautiously optomistic.

 

scooter could make a ton of bucks after the last winter and half selling caution flags

[dryslot]

 

I would actually say that this is the opposite of what has actually happened in most events.

 

 

That would be right, Suppression has won out a lot

[ctsnowstorm628]

I would actually say that this is the opposite of what has actually happened in most events.

With bigger events? Ala 12/29 and 12/27? The weaker s/w not so much, but the more potent ones I thought seemed to trend more potent over time, no?

[Typhoon Tip]

One thing that often gets unnoticed but has a pretty substancial impact this time of the year with regards to mid-latitude synoptic systems is the strength of oceanic subtropical ridging. This gets mentioned a lot during the summer TC season because the strength of subtropical ridging often is the difference between a recurving TC vs. one that might have its sights on a US landfall. 

 

However, their subtle impact in the winter season is probably one that gets overlooked. And we had a brilliant example of that occurring in the disparity in the model guidance yesterday. Lets look at two particular geopotential contours at 500 hPa from the 00z ECMWF and GFS yesterday forecast at 96 hours.

 

 

 

Here we are investigating the 576 dm to get a sense of the subtropical flow, and the 540 dm geopotential height to get a sense of the polar flow. Note that there is actually quite a bit of agreement with the GFS and ECMWF with regards to the strong upper level trough expected to dig into the Pacific NW next week. Where the greatest disagreement lies though is in subtle shifts in the flow downstream, especially eastward of this next polar impulse. Note the subtle ridge off the East US coastline on the ECMWF while the GFS is flat if not showing a trough off the east coast. We all know even in winter, the subtropical ridge likes to rear its ugly head, but in this case, the subtle ridging on the ECMWF is actually helping to promote a more meridional flow regime that could aid cyclogenesis greatly over and off the eastern US coastline. 

 

We talk about this all the time, but sometimes you can go from a merely ordinary shortwave into to something quite dynamic if we get some degree of phasing between the subtropical and polar jets. In the example above, its suggested that the ridging off the east coast allows this potential to be realized with the ECMWF. The GFS can't merge the energy because the flow is too zonal which limits the meridional component of the subtropical shortwave. It really is the subtropical shortwave that is the magic ingredient in this case, because its also providing all the straiform convection that is necessary for mid-level diabatic heating. Diabatic heating from both convective and stratiform precipitation can lead to positive geopotential height perturbations which allow for further ridge amplification. Its a non-linear process that once kicked off, often leads to robust cyclogenesis. 

 

So in short, the Euro is more robust with subtropical ridging, which allows the southern stream shortwave to be strong enough to produce a large precipitation shield, both convective and stratiform. Thanks to this diabatic forcing, the ridge is further amplified, and now the entire system can grow from baroclinic processes (extracting energy from the temperature gradients generated from meridional flow).

 

Since the typical bias is to be too weak with subtropical ridging over the Atlantic, I wouldn't be suprisied to see the GFS continue to trend towards the ECMWF on this particular solution. 

 

 

Toggling those frames like that ... the differences appear entirely related to resolution - the GFS is clearly "blurrier", where the ECM has all kind of discrete features available to interact in, and among the various streams. 

 

This may be a complete lie ... but I thought the GFS's grid was actually more coarse out in time, and that it computes at a higher resolution crossing from middle range into nearer terms.  If there is any truth to that, "perhaps" the stream interaction is merely that finer mesh bringing the event into focus.  

 

But that could be science fiction if the prior statement isn't true. 

 

Either way, that aside ... This thing - as is - has a big time convective aspect upon that 84-hour chart.  You can see that in the QPF, but as suggested by the jet coupling going on at that time between the southern stream system that is curling cyclonically into the eastern/front side of the N stream trough.  That jet max intermingling is going to have a zone of exotic UVM and if that sucker bumped just 50 mile NW there would be a lot of lightning and thunder falling amid some obscenely tall snow fall rate.  

[CoolMike]

People keep talking about this NW trend to these winter storms but from the sidelines I just don't see it.  The first three trackable / shovelable snows trended NW in the last 72 hours but every threat since then has either stubbornly stayed SE/OTS or trended further SE as time went on.

 

That being said this one looks better to me (in an arm-chair quarterback sort of way) than the previous months worth of potential storms.  I'm hoping for a slight NW evolution personally so that SW NH and S VT gets a nice hit.

[Swiscaster]

Even though I just got home to DC from Falmouth, I am going to live vicariously through you guys this week. Rootin for ya!

[N. OF PIKE]

congrats phil on talking about buying a ticket yesterday.

[Tropopause_Fold]

Phil gets a fooking hurricane.

that run essentially goes for my screen name.